counts only living cells; assumes each colony = 1 cell (problem for streptococci); 1 g or 1 ml placed in 9 ml H2O and then diluted by factor of 1:10,000 ; place one ml of solution on plate and count # of colonies, take avg. # colonies and x by 10^4 (or dilution factor); bias due to pH, carbon source, temp., oxygen presence; need to have an idea of what type of bacteria are present in order to use this method

Most Probable Number counts (MPN)

based on some growth parameter like fermentation of lactose for ex.; used to determine # of coliforms in a sample; add sample to lactose broth, determine # of positive tuves (acid + gas), look at statistical table which tells the # of coliforms based on the # of positive tubes

Indirect Method

test for CO2, RNA, DNA, protein to determine if bacteria are growing; technique used in probe to Mars (gave false positive though due to radioactive CO2)

Dath phase- all internal reserves exhausted, cells die- some resistant cells can survive on materials from cells that have lysed (kind of bacterial canabalism= autophagy)- death part of curve and resistant cells show why you must take full course of antibiotics even though you feel better, must kill all of the cells including the resistant ones

D-value

Decimal reduction time- time it takes to kills 90% of a population at a given temperature (canning companies either increase time or temp to kill all cells including resistant ones and endospores)

Temperature range for bacterial growth

-5 to 113+ C

psychrophiles

cold loving; -5 to 15 C; found in super-cooled waters of arctic and antarctic; bacillus, pseudomonas

treponema pallidum causes syphilis, tries to invade CNS, grows just below body temp.; plasmodium vivax is a protozoan that causes malaria, attacks red blood cells and when cell bursts parasite is released, causes fevers of >104; these high temps will kill treponema pallidum and will cure syphilis if patient has syphilis and malaria

x-rays and UV: short range, high intensity and penetrating power
IR: longer wavelength, low intensity w/ little penetrating power
Microwaves: long wavelength- only kill microbes if they generate sufficient heat to do so (microwave ovens do not)

Radiation resistant bacterium

Dienococcus radiodurans- can withstand 1000 x dose that kills e.coli on food and can also repair breaks in DNA; isolated by the army

Filtration

beverages- beer and wine
filters out yeast and contaminants, does not remove viruses (needed a new method to clean up optical solutions)

1846, dr. in ob-gyn ward, made physicians wash up with bleach before delivery b/c women were dying of child birth fever (puerple sepsis) caused by streptococcus pyogenes- dries out hands and painful, but worked

heavy metals

combine with sulfur groups in proteins to denature them
-AgNO3- applied to eyes of newborns to prevent blindness caused by neisseria gonorrhoeae
-Hg used to treat syphilis in 1496; Hg is a major concern in food supply, in fish esp. tuna
-Pb- lead paint causes mental retardation in children
-organic forms of Hg, merthiolate, mercurochrome used as antiseptics

coenzyme- assists an enzyme in metabolism
e. coli can synthesize its own folic acid
sulfa drug looks like PABA which is part of folic acid, but instead prevents e.coli from synthesizing folic acid and carrying out metabolism

lysogenic- 3- viral DNA incorporates into host DNA to become a pro virus

-provirus is a stable genetic element in host DNA
-provirus is copied each time host dna is copied and thus all progeny are infected
-no new virions are made
-host cell is immune to further infections by the same virus
-provirus can alter normal host cell gene function = genetic change
-virus can confer new genetic info on cell = lysogenic conversion
-if nothing perturbs virus (chemicals, UV light, etc.), virun will remain in cell for duration of cell lifetime

cause normal cells to behave like cancer cells
-surface of the host cell becomes like a cancer cell b/c new chemical groups are expressed
-infected cells stop dividing in a controlled fashion and behave like tumor cells

16% of human cancers caused by viruses
How:
1. virus integrates into human DNA, can inactivate a gene or cause the gene to be altered in its expression
2. some viruses carry oncogenes- normal genes picked up by virus, mutation occurs, results in oncogenes in virus- oncogenes take over functions in cells such as cell division causing cell to become abnormal

-antibodies- aggregate virus cells, then WBC's kill viruses
-interferon- protein made by cells infected w/ a virus, inhibits viral replications, released by infected cells and taken up by uninfected cells to protect them

rhino viruses (colds), >100 different viruses
flu- also different viruses and variations of viruses

antigenic DRIFT

type A virus --> mutation to type A1 (ex. mutated spike)

antigenic SHIFT

2 different influenza viruses can infect a cell at the same time- ex. human and avian flus- when virus is assembled a mosaic virus is made (ex. human capsid and avian spike)- immune system thinks it has not seen this virus and immune response must start from scratch